The present invention relates to a process for the production of rigid polyurethane foams having improved demold and outstanding insulation properties.
Processes for the production of rigid polyurethane foams are known. Sucrose-based polyols are of particular interest as the primary isocyanate-reactive reactant because of their relatively low cost, high functionality and because they are relatively simple to produce. Processes for producing such sucrose-based polyols are disclosed, for example, in U.S. Pat. Nos. 3,085,085; 3,153,002; 3,222,357; and 4,430,490. Each of these patents teaches that the disclosed polyols are useful in the production of polyurethane foams.
At the present time, a major concern of foam producers, particularly rigid foam producers, is the development of rigid foam systems in which the chlorofluorocarbon blowing agent is replaced with a more environmentally acceptable blowing agent. HCFCs (i.e., hydrogen containing chlorofluorocarbons), HFCs (hydrogen containing fluorocarbons), and hydrocarbons such as n-pentane cyclopentane, isopentane and blends of these blowing agents are presently considered to be possible alternatives.
U.S. Pat. No. 4,900,365, for example, teaches that a mixture of trichlorofluoromethane, a dichlorofluoroethane selected from a specified group and isopentane is useful as a blowing agent for the preparation of polyurethane foams. Dishart et al's paper entitled "The DuPont Program on Fluorocarbon Alternative Blowing Agents for Polyurethane Foams", Polyurethanes World Congress 1987, pages 59-66 discusses the investigation of various HCFCs as possible blowing agents for rigid polyurethane foams. Neither of these disclosures, however, teaches a process for the production of rigid polyurethane foams having good physical properties from sucrose-based polyols with only an HCFC, an HFC or hydrocarbon blowing agent. In fact, Dishart et al teaches that conventional sucrose-based polyols produced foams which became soft, shrank and in some cases collapsed when HCFC-123 was used as the blowing agent.
A process in which a sucrose-based polyol was used in combination with an HCFC, an HFC or a hydrocarbon blowing agent to produce a rigid polyurethane foam having good physical properties, particularly good demold and insulating properties would, therefore, be advantageous.